[shaders] html -> :root allows CSS var definitions to work.
[shaders] html -> :root allows CSS var definitions to work.

Change-Id: I048f07e066b2f56bb069feb3c091f7253397f6ca
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/496310
Reviewed-by: John Stiles <f4fcf42d3bb5924557f1eeb3be66747535e585da@google.com>
Commit-Queue: Joe Gregorio <b9cf2471ff6d33504cafe8e6f356b732b2cadced@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot